1. Field of the Invention
This invention generally relates to railroad spikes, and more particularly to a novel and improved railroad spike which is actively interconnected with a tie plate hole by being swaged thereagainst, so as to both permit dynamic rail load wave, and minimize the problem of tie cutting while still facilitating spike removal for track maintenance.
2. Brief Description of the Prior Art
The shape of a railroad spike is generally defined by a set of standards, but a standard spike has a shank that is square and nominally 0.625 inches on each side. For example, rail is currently made to meet American Railway Engineering Association (AREA) specification 132 RE for the rail section (1962), and for such rail, Conrail has a standard track spike configuration, Conrail MW 181 (June 28, 1984), that requires conformance to the AREA specifications for Track Spikes, current issue. A railroad spike primarily holds rail gauge by securing a rail flange on top of a tie plate with the tie plate supported on a portion of a wooden tie upper surface. Conventional spike driving equipment almost invariably drives an AREA track spike all the way home, or into contact with the top of the rail flange. Hence, the rail, tie plate and spike become an assembly that initially is tightly fastened together, so that the rail cannot move with respect to either the spike, the tie plate or the tie.
This assembly invariably progressively loosens from dynamic rail load wave. Dynamic rail load wave is well known, and imparts a cyclical, vertical force that gradually pumps a spike out of the tie, causing the spike not only to lose its tie holding power, but also to invite decay in the tie hole. The contact between tie and tie plate also is loosened, and the tie plate than is free to move up down, and sideways (both laterally and longitudinally) thereby applying a pounding and cutting force onto the tie upper surface. The up and down motion occurs every time a train wheel passes over the assembly. While the free, or dynamic rail wave phenomenon is dependent upon the modulus of elasticity of the rail, and also the stability of the underlying rock bed, it has been found that for a 1.0 inch downward deformation of the rail (at mid span between two ties) that instantaneous deformation will cause an approximate 0.050 inch uplift, at the two adjacent tie plate regions. Hence, approximately 5 percent of a mid-span rail downward deflection is translated into an upward, or spike pumping force, that acts directly under the head of a spike that initially was driven into contact with the rail. Rail wave may be thought of as an "Irresistible force", since its magnitude far exceeds any inherent holding forces that can be generated between the shank of a spike and the wooden tie it was driven into.
While certain railroad manuals require a spike to be driven home, others recognize that a vertical spacing between the flange and the spike head of about 0.125 inch may be an optimum gap, so as to avoid the spike pumping phenomenon. However, tie cutting then is permitted to occur, due to horizontal as well as vertical movement of the tie plate, with respect tot he tie. Tie cutting represents a major cost component of railroad maintenance. Loosened spikes must be repeatedly redriven each time they are pumped out by the rail wave, and whole sections of track must be taken out of service when seriously cut ties have to be replaced.
One spike and plate design intended to minimize spike pulling effects of rail wave motion is disclosed in CHENEY (U.S. Pat. No. 1,604,806) wherein a spike shoulder or ear is defined to impart a vertical force on a tie plate, and limit the depth of penetration of the spike into the tie. Therefore, the rail is said to be free to move up and down in accordance with the rail wave. Hence, the special CHENEY tie plate also shows a non-tapered hole, while the holes in the plates used with the present invention typically taper inwardly about 0.10 inch; or from a top width of 0.850 inch to a bottom width of 0.750 inch. Further, CHENEY provides only a minimal point-to-point, shoulder contact with the tie plate, and no structure is available to resist movement of the tie plate forward, backward or sideways as a result of the horizontal forces of rail side loading. Further, it is most probable that an "initial settling" occurs under traffic due to contaminants such as grit or sand which have found their way between the tie plate and tie during installation. The tie plate will immediately disengage itself from the shoulder contact of the spike upon the slightest settling. Therefore, the most damaging, and critical, tie cutting problem is not at all addressed by CHENEY, CHENEY attempts to engage a tie plate upper surface, while the present invention primarily engages two or more surfaces defining the tie plate hole, by a novel swaging action imposed on the spike itself, to resist both lateral and vertical relative movement between tie and tie plate.
Another spike design is represented by WATERMAN (U.S. Pat. No. 791,521) wherein a tie plate hole is said to be made slightly smaller than the spike diameter, in order to prevent relative movement of the rail flange and spike. However, this configuration does not provide any relief to permit the necessary future act of spike pulling. Furthermore, and more damaging, upward and downward forces will now be transferred to both the spike throat and the tie plate, so a "pumping up" rail wave action would even more quickly destroy the holding power of the spike in the tie, while still further aggravating tie cutting.
A detachable spike shoulder used to limit the penetration depth of a conventional track spike into a tie is shown in AMES, U.S. Pat. No. 2,066,382. This detachable element provides only minimal surface contact with the tie plate, and would likely become separated from the spike head, under the forces of a rail wave.
CLARKSON (U.S. Pat. No. 2,271,912) demonstrates a divided shank rail fastener, wherein a rail leg formed at the rear base of the spike head, extending downward and away from the head, is used to limit the depth of penetration of the spike into a tie. Side to side movement of the tie plate will not be prevented by this assembly, since there is no provision for resisting horizontal forces that are incident to the rail load wave.
BOYCE (U.S. Pat. No. 1,837,183) illustrates a tie plate which limits the depth of penetration of a conventional track spike into an underlying tie by means of a shoulder formed in the tie plate. Since the spike used in this rail fastening assembly has a conventional straight shank, it will be eventually dislodged by the irresistible action of a rail wave.